Hydrogen (H2) to be used as a fuel in an anode of a fuel cell is obtained through steam reforming from a hydrocarbon-based fuel such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), naphtha, gasoline, kerosene, or light diesel oil, an alcohol-based fuel such as methanol, or city gas.
A reformed gas obtained through the steam reforming contains, in addition to hydrogen, carbon monoxide (CO) at a significant concentration. The CO contained in the reformed gas causes various problems in the fuel cell. Accordingly, it is necessary to decrease the carbon monoxide concentration in the reformed gas as much as possible before the reformed gas is supplied to the fuel cell.
To that end, hitherto, as one of the methods of decreasing the CO concentration, there has been proposed a method involving converting carbon monoxide into methane (methanation of carbon monoxide) (for example, Patent Literatures 1 to 4).